In the News this month: emission from methane in the atmosphere of an extrasolar planet
This artist concept shows the planetary system called HD 189733, located 63 light-years away in the constellation Vulpecula. CREDIT: NASA/JPL-Caltech
In just fifteen years, several hundred planets have been discovered around stars other than the Sun using a variety of techniques. Even without the ability to directly image these other worlds, some of their properties can be determined. Most extra solar planets found so far are massive gas giants orbiting close to their parent stars, since these are the types of planets that the detection methods are most sensitive to. As techniques develop and improve, astronomers are finding out more and more about these other worlds, including the composition of their atmospheres.
The chemical make-up of planetary atmospheres can provide clues to a whole variety of processes, including both geological and biological effects, but often our own atmosphere gets in the way, hampering attempts to detect the spectral signatures of certain molecules. To get a full picture of what is going on often requires both ground-based and space-based observations. Satellite observations have previously detected the absorption signatures of water, carbon dioxide, carbon monoxide and methane in the atmospheres of two so-called hot Jupiters, planets with masses similar to or greater than that of Jupiter, but orbiting far closer to their parent star.
In research published in Nature on the 4th of February, a team led by Mark Swain of the Jet Propulsion Laboratory in California, have detected the signature of emission from methane in the atmosphere of one particular exoplanet known as HD-189-733-b. Using the NASA Infrared Telescope Facility located on Mauna Kea, the team discovered an unexpectedly strong emission feature at a wavelength of 3.25 microns, corresponding to the presence of methane in the planet's atmosphere.
This is not the first time that methane fluorescence has been seen, but it is the first time it has been detected in the spectrum of an exoplanet. It has previously been seen in our own solar system in the atmospheres of Jupiter, Saturn and Titan, although HD-189-733-b is much closer to its parent star and so offers a chance to study a planetary atmosphere under very different physical conditions.
This blog post is a news story from the Jodcast, aired in the March 2010 edition.
Swain, M., Deroo, P., Griffith, C., Tinetti, G., Thatte, A., Vasisht, G., Chen, P., Bouwman, J., Crossfield, I., Angerhausen, D., Afonso, C., & Henning, T. (2010). A ground-based near-infrared emission spectrum of the exoplanet HD 189733b Nature, 463 (7281), 637-639 DOI: 10.1038/nature08775